That said, all of those professional services are directly hirable by any musician, without the need for a label middleman. The best move a band can make, is hire someone to handle the thing they least want to do. As you mentioned, posting on social media is the most hated of all tasks for a lot of folks, and in that situation your first hire should be a publicist (aka social media manager). It gets the largest monkey off your back, and frees up that time for all of the other business stuff that still needs to get done.
That said, you could also hire a publicist for a day, and they could assemble a social media schedule for you, and provide a bunch of templates to use, and take all of the mystery out of what to post and when and how and why. And now instead of paying a retainer or sharing gross, you're paying someone in the band to do it, and all of the money stays with the group.
As for your prediction, you're correct about that, as well, because it's already starting to happen. Many people, like myself, offer a sort of label/manager on-demand service, where for a very small consultation fee, the band gets a monthly analysis of where they're at and what steps they need to be taking, along with all of the granular instructions on how to accomplish those tasks. If I had to guess, there are currently about 1,000 people doing this around the world, but that number is growing rapidly. There are also a lot of tools springing up to help simplify those tasks.
As for learning, YouTube is your best friend. There's a mountain of music business content on there, and most of it is very accurate to reality.
https://www.youtube.com/c/berkleemusic/videos
My prediction is that there's a pendulum back-swing in progress as people figure out how to offer brand-management-as-a-service without just becoming a label.